Proton transfer in aminocyclopentadienyl ruthenium hydride complexes

A new ruthenium hydride complex of the aminocyclopentadienyl ligand (Cp-N)R uH(PPh3)(2) (Cp-N = C5H4CH2CH2NMe2, 1) has been prepared and characterized by X-ray diffraction. Protonation of 1 with excess HPF6 leads to the dicati onic derivative [(Cp-NH)RuH2(PPh3)(2)](PF6)(2) (2), in which both the metal and the amino substituent have been protonated. Addition of 1 equiv of HBF 4. Et2O to 1 leads to the complex [(Cp-N)Ru(PPh3)(2)](BF4) (3), containing a chelating amino cyclopentadienyl ligand after elimination of Ha However, using (HNEt3)(BPh4) or (HPBu3)(BPh4) as protonating agent, it is possible t o form [(Cp-NH)RuH(PPh3)(2)](BPh4) (4), which was isolated as yellow crysta ls of 4 . H2O upon addition of undistilled methanol and characterized by X- ray crystallographic analysis. A fluxional process exchanging the ammonium proton and the hydride without changing the thermodynamic state of the syst em could be established by H-1 NMR, and activation energies of 11 kcal.mol( -1) were calculated for 4 . H2O and the product resulting from in situ addi tion of [HNEt3][BPh4] to 1, whereas an activation energy of 10.1 kcal.mol(- 1) was found for the product resulting from in situ addition of [HPBu3][BPh 4] to 1. A density functional study (B3PW91) was carried out, and the dihyd rogen bond in the model system for 4 was calculated to be 1.545 Angstrom, i n excellent agreement with T-1 measurements (1.52 Angstrom). The proposed m echanism for the fluxional process does not involve a proton transfer withi n the dihydrogen bond.